/in/foo.cc: In function 'int main()':
/in/foo.cc:18:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int i = 1; i < s.size(); i++)
                             ~~^~~~~~~~~~
/in/foo.cc:53:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int i = 0; i < s.size(); i++)
                             ~~^~~~~~~~~~
/in/foo.cc:14:14: warning: variable 'flag' set but not used [-Wunused-but-set-variable]
         bool flag = false;
              ^~~~